1. Field of the Invention
The invention relates to a light emitting device. More particularly, the invention relates to an organic light emitting device.
2. Description of Related Art
The organic light emitting device (OLED), with advantages such as self-luminescence, wide view angle, low power consumption, simple manufacturing process, low cost, low operation temperature range, high responsive speed and full colors, has a great potential of becoming the mainstream flat panel display product in its next generation.
In general, the organic light emitting device includes a first substrate, an organic light emitting unit disposed on the first substrate, and a second substrate sealing and packaging the organic light emitting unit with the first substrate, wherein the organic light emitting unit includes a light emitting layer sandwiched between two electrodes. A light emitted from the light emitting layer may be restricted inside the organic light emitting device owing to the total internal reflection (TIR) effect of the substrate when the light emits obliquely out from the first substrate or the second substrate at large angle so that the light emitting efficiency of the organic light emitting device is limited.
Recently, the light emitting efficiency of the organic light emitting device has been improved by several techniques. For example, a micro lens array or a plurality of microstructures is provided to be formed on the surface of the substrate by an adhesion process. Nevertheless, this method may be unfavorable to the fabrication of the organic light emitting device because of the misalignment and the poor adhesion between the substrate and the microstructure during the additional adhesion process. Alternately, a layer of photonic crystal structure or a grating with low refractive index is provided to be disposed between the substrate and the light emitting layer. However, the film layer uniformity of the organic light emitting unit formed on the layer of photonic crystal structure or the grating with low refractive index is poor to cause an over large electric field in a particular region, which may shorten the lifetime of the organic light emitting device. Accordingly, the issue of the organic light emitting device to be overcome by the researchers lies in the improvement of the light emitting efficiency without influencing on the lifetime and complicating the fabrication thereof.